Alpha-glucosidase (E.C 3.2.1.20) (also known as acid maltase glucoinvertase, glucosidosucrase, maltase-glucoamylase, α-glucopyranosidase, glucosidoinvertase, α-D-glucosidase, acid alpha glucosidase, α-glucoside hydrolase, and α-1,4-glucosidase) (GAA) is an enzyme involved in hydrolysis of terminal, non-reducing (1→4)-linked α-D-glucose residues with the release of α-D-glucose. A deficiency of this enzyme results in Pompe disease (also known as glycogen storage disease type II, GSD II/GSD 2, type 2 glycogenosis, acid maltase deficiency, alpha glucosidase deficiency, alpha-1,4-Glucosidase deficiency, cardiomegalia glycogenica diffusa, generalized glycogenosis, lysosomal alpha glucosidase deficiency or lysosomal glucosidase deficiency), which is an autosomal recessive lysosomal storage disorder. Pompe disease is characterized by pathological accumulation of glycogen in lysosomes of multiple tissues (Hirschhorn and Reuser, Glycogen Storage Disease Type II: Acid a-Glucosidase (Acid Maltase) Deficiency, Internet Computer File Date of Entry: 20090331, New York: McGraw-Hill (2009)—available from: URL: genetics-dot-accessmedicine-dot-com/). Myocytes within skeletal, cardiac and smooth muscles are disproportionately involved. Glycogen accumulation in these tissues can occur rapidly. Glycogen accumulation has been detected in fetuses as young as 16-18 weeks gestational age (Hug 1978; Phupong, Shuangshoti et al. 2005).
The classical, infantile form of Pompe disease is considered the most severe within the spectrum of Pompe phenotypes and is characterized by cardiomyopathy, hypotonia, and respiratory insufficiency. Many infantile Pompe disease patients are living longer and are experiencing enhanced quality of life as a result of rhGAA (alglucosidase alfa, Myozyme®, Lumizyme®, Genzyme Corporation, Massachusetts, USA) enzyme replacement therapy (ERT) (Kishnani et al, Neurology 68(2):99-109 (2007), Kishnani et al, Pediatr. Res. 66(3):329-335 (2009), (Kishnani, Corzo et al. 2007; Kishnani, Corzo et al. 2009; Nicolino, Byrne et al. 2009) (see also U.S. Pat. No. 7,056,712). Without effective ERT with rhGAA, death typically occurs secondary to cardiorespiratory failure within the first one to two years of life (van den Hout, Hop et al. 2003; Kishnani, Hwu et al. 2006; Hirschhorn and Reuser 2009). This is in contrast to the juvenile and adult-onset forms (late-onset Pompe disease), where skeletal and respiratory muscle weakness predominates. Overall, there is an inverse correlation between disease severity and the level of residual enzyme activity. The most severely affected individuals have little to no detectable GAA activity. Such patients typically present during infancy (Hirschhorn and Reuser 2009).
In addition to GAA activity, there are additional factors known to affect outcome in patients with Pompe disease. These include, but are not necessarily limited to, age upon ERT initiation, extent of preexisting pathology, the degree of muscle damage as well as the muscle fiber type (i.e., type I vs. type II) with greatest relative involvement as well as defective autophagy (Kishnani, Nicolino et al. 2006; Hawes, Kennedy et al. 2007; Kishnani, Corzo et al. 2007; Raben, Takikita et al. 2007).
ERT with rhGAA is the only definitive treatment for Pompe disease. This therapy is often complicated by immune responses to the enzyme which can block efficacy and cause severe adverse outcomes by formation of anti-rhGAA antibodies.
It has been shown that CRIM status carries significant prognostic value in treatment response. Relative to most CRIM-positive patients, CRIM-negative patients tend to do poorly with regard to response to ERT. In CRIM-negative patients, there exist two deleterious GAA mutations that result in no production of native enzyme. Concurrent with clinical decline, persistently elevated anti-rhGAA IgG antibody titers have been seen in CRIM-negative patients while titers for most CRIM-positive patients remained relatively low in comparison (Kishnani, Goldenberg et al. 2009). However, there is a subset of CRIM-positive patients (infants, juveniles and adults) who also develop high sustained anti-rhGAA antibody titers and have a poor clinical outcome. (Banugaria et al. 2011) That CRIM-negative patients generate antibody responses that are unremitting and abrogate the efficacy of a life-saving therapeutic has required the development of clinical protocols to induce tolerance. These protocols and variations thereof are ideally implemented prophylactically or simultaneously with the onset of treatment and before the development of untoward levels of antibody titers against the therapy.
Tolerance-inducing therapies have been explored in experimental animal models and are being implemented for patients who have developed or have a high risk of developing life-threatening antibody response to ERT.
For ongoing antibody responses in the CRIM-negative Pompe setting, in which nephrotic syndrome may be induced by continued administration of enzyme, and which if treated with ERT alone results in clinical decline and death, tolerance-inducing therapies have a favorable risk-benefit ratio. However, in this situation, the immune suppression may be even more intensive and extensive because antibody levels must be markedly reduced to reverse/prevent further clinical deterioration and complications such as nephrotic syndrome and to facilitate tolerance induction. When ERT fails as a result of antibodies, and patient outcome is death or severe disability or impairment (such as ventilator dependency), vigorous therapeutic efforts at eliminating immunity based on the best available experimental and clinical studies is warranted (Wang, Lozier et al. 2008). At this time, there is no agent that has shown success in reducing antibody titers once a patient has high and or persistent antibody titers.
Therapies to trigger inhibitory FcR expressed on B cells and antigen-presenting cells and to target B-cell survival and activation factors (such as B-cell activating factor and B-lymphocyte stimulator) are under development. Depleting approaches using rituximab, a chimeric monoclonal antibody with human IgG1 constant domains that depletes mature B cells expressing the CD20 molecule, can be of use in the prophylaxis setting, potentially allowing introduction of enzyme at a stage when immature enzyme-specific pre- and pro-B cells can be deleted or rendered nonresponsive. Combinations of rituximab and antibodies to B-cell activating factor continue to be of interest (Wang, Lozier et al. 2008). Immune modulation with the anti-CD20 monoclonal antibody rituximab plus methotrexate and intravenous gamma globulin in a CRIM-negative patient has resulted in tolerance induction (Mendelsohn, Messinger et al. 2009). However, this patient did not have high sustained antibody titer at the start of treatment. More difficult than inducing tolerance in a naive setting is the task of reversing an ongoing robust immune response. Studies suggest that rituximab interrupts the pathways driving development of plasma cells and that not all plasma cells have an equally long life span. However, it is not clear whether true tolerance is induced in these settings. Notably lacking from the therapeutic armamentarium are antibodies to target long-lived plasma cells, the elimination of which may be vital in reversing entrenched immune responses (Wang, Lozier et al. 2008). Treatment with rituximab in kidney transplant patients as well as in other disease where high amounts of antibodies are formed against the donor tissue or protein, failed to decrease the antibody titers in those patients. (Everly, Everly et al. 2008)
Gene therapy with vectors (viral or non-viral) is sometimes complicated because of an immune response against the vector carrying the gene. The plasmids used for nonviral gene therapy, alone or in combination with liposomes or electrotransfer, can stimulate immune responses (Bessis, GarciaCozar et al. 2004). Viral vectors are the most likely to induce an immune response, especially those, like adenovirus and adeno-associated virus (AAV), which express immunogenic epitopes within the organism. (Bessis, GarciaCozar et al. 2004). Various viral vectors are used for gene therapy, including but not limited to retroviruses for X-linked severe combined immunodeficiency (X-SCID), adenoviruses for various cancers, adeno-associated viruses (AAVs) to treat muscle and eye disease, lentivirus, herpes simplex virus in nervous system. Anytime a viral vector is introduced into human tissues, the immune system reacts against the vector. The risk of stimulating the immune system in a way that reduces gene therapy effectiveness is always a possibility. Furthermore, the immune system's enhanced response to vectors that it has seen before makes it difficult for gene therapy to be repeated in patients. Furthermore, in general, population antibodies against AAV are formed because of natural exposure and results in antibodies from all four IgG subclasses whereby AAV vector mediated gene therapy in these patients makes it difficult to get a desired response (Boutin, Monteilhet et al. 2010).
Also with gene-therapy, antibodies are formed against the actual protein produced by gene-therapy and these antibodies can reduce efficacy. For example, in a Pompe disease knock-out mouse model (GAA-KO), treatment with AAV2/8 (adeno associated virus vector) containing hGAA under the control of CMV enhancer/chicken B-actin (CB) promotor (AAV-CBhGAApA) resulted in enzyme production in various tissues but this therapy was complicated by high antibody production against the enzyme produced by the gene (Franco, Sun et al. 2005). Immunomodulatory gene therapy in the naïve setting (before the exposure with enzyme replacement therapy) with AAV-LSPhGAApA induces immune tolerance in GAA knock-out mice and regulatory T cells (Treg) were demonstrated to play a role in the tolerance induced by gene therapy (Franco, Sun et al. 2005; Sun, Bird et al. 2007) (see also Sun et al. 2010) but it failed to do so in a setting where significant immune-response had already taken place (as evident by presence of high antibody titers) as described in Example 1 below. This vector therapy could be acting by its possible mechanism on Treg cells but it could be possibly compromised in inducing immune tolerance because of pre-existing plasma cells which continue to produce antibodies.
Immunity against vectors and their contents can substantially reduce the efficiency of gene therapy. A strong immune response against the constituents of the vector or the transgene leads to rejection of the cells infected by the vector and, therefore, to a reduction in the duration of expression of the therapeutic protein (Manno et al. 2006).
Bortezomib is a proteasome inhibitor that acts against both short-lived and long-lived plasma cells. It is FDA approved for the treatment of plasma cell derived tumors—multiple myeloma. Everly et al demonstrated the first clinical use of bortezomib as an anti-humoral agent in treating mixed antibody-mediated rejection (AMR) and acute cellular rejection (ACR). It provided the effective treatment of AMR and ACR with minimal toxicity and sustained reduction of antibodies. The activity of bortezomib against mature, antibody-secreting plasma cells underlies its efficacy in suppressing antibodies by eliminating the source of antibody production (Everly, Everly et al. 2008). Because of extensive immunoglobulin production by plasma cells, proteasome inhibition induces plasma cell depletion as a result of activation of the terminal unfolded protein response (UPR). Late inhibition of anti-apoptotic transcription factor NF-kB may contribute to bortezomib induced plasma cell death (Neubert, Meister et al. 2008).
The present invention provides a method of reducing/preventing antibody titers and/or providing clinical benefit to patients undergoing protein (e.g., enzyme) replacement therapy (PRT). The invention results, at least in part, from studies demonstrating that the proteasome inhibitor, bortezomib, decreases antibody titers by eliminating the source of antibody titer formation, that is, long- and short-lived plasma cells. The invention also relates to methods of reducing antibody titers or preventing the formation of antibody titers and/or for clinical benefit in other settings (including gene therapy) where antibodies complicate therapeutic goals.